1. Field of the Invention
The present invention relates to electromagnetic fuel injection values, and particularly, to electromagnetic fuel injection valves suitable for use with a gaseous fuel, such as compressed natural gas fuel or similar fuels.
2. Description of the Related Art
A known fuel injection value using electromagnetic force has been disclosed in Japanese Laid-Open Patent Publication No. 4-31662. In this fuel injection valve, a movable valve for opening and closing a fuel injection port is supported by a flat spring. The movable valve is usually biased to close the fuel injection port (valve closing direction) by the elastic force of a coil spring. In this state, when electric power is supplied to a solenoid coil, the movable valve moves in a direction (valve opening direction) that opens the fuel injection port as a result of the electromagnetic attraction force.
In the known fuel injection valve, a magnetic circuit for generating the electromagnetic attraction force has two air gaps between the movable valve and a magnetic circuit-forming member. In this fuel injection valve, the amount of the electromagnetic attraction force that is generated is proportional to the area of the movable valve surface that faces each air gap and to the area of the surface of the magnetic circuit forming member. Therefore, in order to improve the operating response of the movable valve, the area of the movable valve surface that faces the air gap and the area of the magnetic circuit forming member surface most be increased so as to increase the electromagnetic attraction force.
However, if the movable valve surface and the magnetic circuit forming member surface are increased, the size of the fuel injection valve will also increase. Because the fuel injection valve is mounted to an engine, it is not preferable to increase the size of the fuel injection valve. Moreover, because the supply voltage (valve operating voltage) that must be applied to the solenoid coil in order to move the movable valve also must increase in order to increase the electromagnetic attraction force, the generation efficiency of electromagnetic attraction force is reduced.
Furthermore, in the known fuel injection valve of Japanese Laid-Open Patent Publication No. 4-31662, the flat spring comes in metal contact with the movable valve. Thus, the flat spring and the movable valve will rub against each other when the movable valve performs the valve opening and closing operation. For this reason, the movable valve and the flat spring are quickly worn and the durability of the valve is reduced.
In order to prevent the movable valve and the flat spring from being worn, the flat spring can be fixed to the movable valve. However, when the flat spring is fixed to the movable valve, stress is applied to the flat spring when the movable valve performs the valve opening and closing operation. When the applied stress is large, a weak portion of the flat spring may break. For this reason as well, the durability of the known electromagnetic valve is reduced.
In one aspect of the present teachings, an electromagnetic valve is taught that generates an electromagnetic attraction force acting on a movable valve by a magnetic circuit having air gaps. The dimensions of the air gaps are selected in order to reduce the valve operating voltage, thereby improving the valve operating performance and permitting the size of the valves to minimized.
In another aspect, a movable valve and flat spring are taught that reduce or prevent the possibility of unnecessary wear on the fuel injection valve, which is used to open and close a fuel injection port. An elastic member may be disposed between the movable valve and the flat spring to reduce wear on the flat spring. Thus, it is possible to make a fuel injection valve that has high durability.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.